The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Gunman's target may have been Seven

The Sydney siege gunman's bizarre and troubling behaviour in the years leading to his death appeared to have been sparked by a program aired by the Seven Network, leading to speculation his intended target was the broadcaster's Martin Place studios.

The revelations come amid reports Man Haron Monis may have been spooked by heavy security at the TV network's offices on Monday morning and decided instead to take 18 people hostage in the nearby Lindt Chocolat cafe, in a siege that ended with the death of the gunman and two of his captives.

Monis's former lawyer Manny Conditsis says the self-proclaimed sheik had in July, 2007 been angered by what he saw as anti-Muslim comments on the Sunrise program.

The popular breakfast show was covering the arrest of Indian doctor Mohamed Haneef in Australia following the failed terrorist attacks in London and Glasgow.

Monis felt a commentator on the program was drawing offensive links between Dr Haneef, who was later cleared of any links to terrorism, and the Glasgow bomber who was also a Muslim doctor.

"Attention please attention, a ridiculous message for Muslim doctors: If you want to kill people, why not use the tools of your own trade like a plague or a disease or something? Why go into an area which you're clearly unqualified in?" (Sunrise broadcast 4th July 2007, Australian TV, Channel 7)," Monis posted on his website at the time.

Monis made many more references to Sunrise and the Seven Network throughout his site, which has since been taken down.